1. Field of the Invention
The present invention relates to a short-arc type high pressure discharge lamp and a lamp apparatus including the same.
2. Description of the Related Art
A short-arc type high pressure discharge lamp has been used as a light source of a projection type projector. FIG. 1 is a sectional view showing a short-arc type high pressure discharge lamp in related art; FIG. 2 is a sectional view showing a manufacturing process of a short-arc type high pressure discharge lamp in related art; FIGS. 3A through 3C are A-A line cross-sectional views of FIG. 2; FIG. 4 is an enlarged view showing portions of an electrode axis and a sealed metal foil; and FIG. 5A is an enlarged view showing the portions of the electrode axis and sealed metal foil and FIG. 5B is an enlarged view showing the inside of a circle in FIG. 5A.
As shown in FIG. 1, a short-arc type high pressure discharge lamp 10 includes: a discharge container 12 made of glass material such as quartz glass, a pair of electrodes 14, and two sealed metal foils 16. The discharge container 12 is formed of a pair of axis portions 1202 and a swelled portion 1204 provided between the pair of axis portions 1202 and having a sealed space 20 inside in which mercury and the like are enclosed.
Each of electrodes 14 has an electrode axis 1402 and an electrode body 1404 provided at an end of the electrode axis 1402. With respect to the pair of electrodes 14, the electrode axes 1402 are buried in the pair of axis portions 1202 respectively and the electrode bodies 1404 are disposed to face each other in the sealed space 20. Two sealed metal foils 16 extend like a strip having a narrow width and are buried in the axis portions 1202 such that the longitudinal direction thereof is parallel to the longitudinal direction of the axis portion 1202. The electrode axis 1402 is joined to one end in the longitudinal direction of the sealed metal foil 16 by resistance welding, and a lead wire 18 is joined to the other end in the longitudinal direction by the resistance welding. When lighting the short-arc type high pressure discharge lamp 10, on connecting an outside power source to each lead wire 18 and on applying a voltage to each electrode 14, an electric discharge occurs between the electrode bodies 1404 to make the sealed space 20 become a high temperature exceeding 300° C., mercury in the sealed space 20 is vaporized to be a mercury vapor pressure of around 200 atmospheric pressure for example, and light is emitted by an arc discharge occurred between the electrode bodies 1404 in that state.
The above short-arc type high pressure discharge lamp 10 is manufactured as follows. First, as shown in FIG. 2, a glass tube 22 whose diameter is larger than that of the axis portion 1202 of the discharge container 12 is prepared. The glass tube 22 has a pair of small diameter portions 2202 having an inner diameter larger than the width of the sealed metal foil 16, and a large diameter portion 2204 provided between those small diameter portions 2202 and having a larger inner diameter than the inner diameter of the small diameter portion 2202. First, with mercury as a base Ar gas and halogen gas are injected into the large diameter portion 2204. Next, each of the pair of electrodes 14 to which the sealed metal foil 16 is welded is inserted respectively from each of small diameter portion 2202 of the glass tube 22 toward the large diameter portion 2204 to make the electrode bodies 1404 face each other in the large diameter portion 2204. At that time, the electrode axis portion 1402 welded to the sealed metal foil 16 is positioned in the small diameter portion 2202 as shown in FIGS. 2 and 3A.
Next, the end portion of each small diameter portion 2202 positioned on the side opposite to the large diameter portion 2204 is irradiated with a laser light beam and is heated to fuse the end portions of the small diameter portions 2202 positioned around the lead wires 18 and so both ends of the glass tube 22 are sealed. Hence, the sealed space 20 hermetically sealed is formed inside the large diameter portion 2204. Next, while cooling down the mercury in the sealed space 20 to prevent evaporation thereof by exposing the large diameter portion 2204 to liquid nitrogen, laser light beams are applied moving from the end portion of each small diameter portion 2202 toward the large diameter portion 2204 and so the whole area of the small diameter portion 2202 is sequentially heated. Hence, the portion of the small diameter portion 2202 around the lead wire 18 and the portion of the small diameter portion 2202 around the sealed metal foil 16 are fused. At this time, a barometric pressure inside the discharge container 12 is equal to or lower than the atmospheric pressure, because the large diameter portion 2204 is cooled down with the liquid nitrogen. Accordingly, as shown in FIG. 3B, the fused small diameter portion 2202 is shrunk to have a small outer diameter due to the difference in the pressure.
Further, when the inner surface of the fused small diameter portion 2202 contacts with both ends in the widthwise direction of the sealed metal foil 16, the inner surface of the fused small diameter portion 2202 shrinks to come close toward the sealed metal foil 16 in the direction orthogonal to the widthwise direction of the sealed metal foil 16 as shown in FIG. 3C, because the sealed metal foil 16 serves as resistance. Then, the portion of the fused small diameter portion 2202 wraps the electrode axis 1402 and sealed metal foil 16 to be in a state where, as shown in FIG. 4, the portion of the fused small diameter portion 2202, that is, the fused glass material portion closely contacts with the whole area of the rear surface 1604 on the side opposite to a surface 1602 of the sealed metal foil 16 to which the electrode axis 1402 is welded. Further, a fused glass material portion 12A closely contacts with a portion of the outer circumferential surface 1402A on the side opposite to the sealed metal foil 16 in the outer circumferential surface 1402A of the electrode axis 1402. The short-arc type high pressure discharge lamp 10 as shown in FIG. 1 is obtained in this manner.
Hereupon, as shown in FIGS. 5A and 5B, since the glass material portion 12A may not fully enter on both sides of the electrode axis 1402 between the outer circumferential surface 1402A thereof and the surface 1602 of the sealed metal foil 16 to which the electrode axis 1402 is welded, gaps S are formed respectively. The gap S is continuous with the sealed space 20. Further, it is illustrated in FIG. 5A that the fused glass material may closely contact with half the outer circumferential surface 1402A of the electrode axis 1402 on the side opposite to the portion to which the sealed metal foil 16 is welded, however, the gaps S on both sides of the electrode axis 1402 are in actuality continuous with each other through the half portion of the outer circumferential surface 1402A of the electrode axis 1402. The gaps S on both sides of the electrode axis 1402 are formed to be gradually small in the direction away from the electrode axis 1402 and along the surface 1602 of the sealed metal foil 16, and a surface 12-1 of the glass material portion 12A facing the gap S forms an acute angle θ with the surface 1602 of the sealed metal foil 16. Therefore, when the short-arc type high pressure discharge lamp 10 is lit, mercury vapor pressure rises in the sealed space 20 and so pressure in the gap S also rises, and strong force almost like a wedge acts on a portion of a gap S1 that is the acute angle θ formed by the surface 12-1 of the glass material portion 12A facing the gap S and the surface 1602 of the sealed metal foil 16.
Then, a crack may occur from that portion of the gap S1 along the boundary surface between the surface 1602 of the sealed metal foil 16 and the surface 12-1 of the glass material portion 12A, which is a disadvantage on improving the durability of the short-arc type high pressure discharge lamp 10. In order to solve such problem, it has been proposed to change the shape of the sealed metal foil 16 (refer to Patent Reference 1). FIG. 6A is a plan view showing portions of the electrode axis 1402 and the sealed metal foil 16 in an example of related art in which the shape of the sealed metal foil is changed; and FIG. 6B is a BB-line cross-sectional view of FIG. 6A. As shown in FIGS. 6A and 6B, the sealed metal foil 16 is wrapped up to a portion opposite to a portion welded to the sealed metal foil 16 along the outer circumferential surface 1402A of the electrode axis 1402 in the portion where the electrode axis 1402 is welded to the sealed metal foil 16 and so the gaps S formed on both sides of the electrode axis 1402 between the outer circumferential surface 1402A thereof and the surface 1602 of the sealed metal foil 16 are eliminated.
[Patent Reference 1] Japanese Patent No. 3518533